/Engine/Source/Runtime/Core/Public/Misc/MonotonicTime.h
This is a monotonic clock which means the current time will never decrease. This time is meant primarily for measuring intervals. The interval between ticks of this clock is constant except for the time that the system is suspended on certain platforms. The tick frequency will differ between platforms, and must not be used as a means of communicating time without communicating the tick frequency together with the time.
struct FMonotonicTimePoint